In most molten metal refining processes, including processes for making steel, aluminum, brass and the like, a molten slag is produced. Because molten slag generally has a density which is lower than the molten metal, it generally floats and accumulates above the upper surface of the molten metal within a processing vessel. The slag provides for essential metallurgical functions such as the absorption of certain elements desired to be removed from the molten metal or the creation of an environment in which elements may be added to the molten metal by methods such as oxide reduction in the slag and may be later transferred to the metal. In other applications the slag serves as a reaction site which facilitates certain chemical reactions which are necessary or desirable in order to efficiently process the molten metal from its initial, crude state to a finished product. In the metal making industry, it is important to monitor the chemical and/or metallurgical composition of the refined slag in order to effectively monitor the molten metal processing. Thus, it is necessary to efficiently collect and timely analyze the slag in order to properly control the metal refining process.
A traditional method for obtaining a sample of metal refining slag from a molten metal bath in a processing vessel is to immerse a metal object, such as a pipe, a metal spoon, a metal chain or the like into the slag for a predetermined relatively short period of time. Because of temperature variations, a layer of the molten slag is chilled onto the cooler metal object so that upon removal of the metal object from the processing vessel, the solid slag may be conveniently broken away from the metal object, collected and promptly analyzed using known analytical methods and techniques.
It is also common in the metal producing industry to monitor various other qualities of the molten metal in a processing vessel such as temperature, viscosity, temperature of solidification (liquidest arrest temperature) and carbon, oxygen and other component content. Many different types of devices or probes have been developed and used for this purpose. Many such devices have a common feature, namely they generally employ a hollow cardboard tube which serves as a probe body for supporting one or more sensors and/or samplers to allow the sensors and/or samplers to be inserted into the molten metal at a desired depth below the refining slag to obtain the necessary data and/or samplers. Because of the hostile environment in which the sensors operate, most such sensors are disposable, having a life on the order of only a few seconds. In general, the cardboard tube supporting the sensors is continually combusted during the time that the sensors are in the molten metal bath.
Traditionally, such disposable sensors are inserted into the molten metal bath manually by an operator using steel pipes which have been adapted with electrical contacts and wiring for electrically passing signals received from the sensors mounted on the first or immersion end of the cardboard tube. In other applications the manual, operator immersion of the expendable sensor is replaced with a mechanical manipulator or pantograph which interconnects with the distal or upper end of the cardboard tube and is employed for automatically lowering the tube and sensors into the molten metal bath at a predetermined immersion depth.
It has become well-known to secure a generally cylindrical metal object to the cardboard tube on a immersion probe for the purpose of collecting a sample of the slag as the sensor measurements are made. Typically such metal objects, such as metal tubes or metal coils, are permanently secured to the cardboard tube at a stationary position, generally a predetermined distance from the first or measurement end of the cardboard tube or probe body. In this manner, when the probe body is inserted or immersed into the molten metal bath for making the required measurement, a sample of the slag can be simultaneously obtained and recovered when the probe body is removed from the metal bath.
While this method of obtaining slag samples can be useful in some applications, it is sometimes difficult to use because it requires that the operator very carefully judge the precise location of the slag and its depth so that the metal object used for collecting the sample of the slag is, in fact, maintained in the slag layer and does not pass through the slag into the molten metal below. It is often difficult for an operator to make such a judgment because of the bright, sometimes blinding, light emitted by molten materials at high temperature. It is even more difficult for an operator to judge the correct placement of the slag collecting metal object because the volume of molten metal in a refining vessel or transferring container is not generally reproducible from batch to batch so that the location (depth) of the slag layer also varies from batch to batch. When an automatic or pantograph immersion system is employed, constant adjustment is required to adapt to the changing volumes of the molten metal in order to obtain proper slag samples. If the slag collecting metal object is immersed too deeply, the slag collecting object can be destroyed by the molten metal. If the slag collecting metal object is not immersed deeply enough to be within the slag layer, either insufficient slag is collected or no slag is collected at all.
The present invention overcomes the problems of the prior art slag sample collecting methods by eliminating the need for an operator determining the exact depth of immersion or exact location for fixing the slag collecting metal object by allowing the slag collecting metal object to "float" or move up and down the cardboard tube of the immersion probe. The movement of the slag collecting metal object assures that the slag collecting metal object is at a position of maximum exposure to the slag while keeping the slag collecting metal object out of the molten metal. The range of movement of the slag collecting metal object is contained at the lowermost or first and uppermost or distal ends of the probe body. Optimum buoyancy is obtained by the combination of two materials, a slag collecting or chill material, generally metal and a second material of a density less than the density of the molten metal. In this manner, the average density of the resulting combination of the two materials is less than the density of the molten metal for any given type of metal and greater than the density of the refining slag to be sampled.